Crank gearing with a special crosshead for high pressure reciprocating compressors

ABSTRACT

A crosshead frame structure is formed from two identical elongated rigid frame sections, each having spaced sidewalls interconnected by spacing blocks at the opposite ends thereof and reinforced by longitudinally extending ribs. The frame sidewalls enclose a connecting rod and have openings for rotatably mounting the connecting rod gudgeon and accommodating the movement of a crankshaft connected to the connecting rod. A pair of plate members mounted between the frame sections on either side of the crankshaft opening serve to mount a pair of piston rods and further include wing portions in a horizontal plane containing the motion axis of the piston rods. Also, a pair of vertical plate portions are mounted to the lower frame section of the crosshead in a vertical plane containing the motion axis of the piston rods. Corresponding horizontal and vertical guide means secured to the housing for the crosshead guide the crosshead structure in horizontal and vertical planes containing the motion axis of the piston rods.

United States Patent Inventor Costantino \"inciguerra 1,620,870 3/1927Carrey' 230/192X Virenze, Italy 2,236,853 4/1941 Herzmark..... 230/185Appl. No. 823,094 2,404,079 7/1946 Manicalco et al. 230/185 5253 r33;Primary Examiner-Robert M. Walker 7 Assignee Nuovo Pignone S.p.A.Attorney-Ralph Watson Firenze, Italy Pnomy 1969 ABSTRACT: A crossheadframe structure is formed from two Italy identical elongated rigid framesections, each having spaced 835,185/69 sidewalls interconnected byspacing blocks at the opposite ends thereof and reinforced bylongitudinally extending ribs. The frame sidewalls enclose a connectingrod and have CRANK GEARHNG WITH A SPECIAL CROSSHEAD openings forrotatably mounting the connecting rod gudgeon FOR COM PRESSORS HIGHPRESSURE RECIPROCATING and accommodating the movement of a crankshaftconnected to the connecting rod. A pair of plate members mounted betweenthe frame sections on either side of the crankshaft 5 Claims 4 DrawingFlgs' opening serve to mount a pair of piston rods and further in- U.S.CI elude portions in a horizontal plane containing the mo.

[ 21/22 tion axis of the piston rods. Also, a pair of vertical plateporof Search I 85, tions are mounted to the lower frame section of thecrosshead 103/171, 184; 417/521373 in a vertical plane containing themotion axis of the piston rods. Corresponding horizontal and verticalguide means [56] References cued secured to the housing for thecrosshead guide the crosshead UNITED STATES PATENTS structure inhorizontal and vertical planes containing the mol,432,04l 10/1922 Scott.Q 103/171 tion axis of the piston rods.

SHEET 1 OF 4 I N VE N TOR :PATENTEUJUM usn 3.581,583

SHEET 2 BF 4 INVENTOR.

' PATENTED UN nan 3,5 1 5 3 sum 3 or 4 CRANK GEARING WITH A SPECIALCROSSHEAD FOR HIGH PRESSURE RECIPIROCATING COMPRESSORS The presentinvention relates to a crank gear with a crosshead suitable to operatethe pistons of high-pressure reciprocating compressors. The mainlimiting factor for attaining high pressures--; with a reciprocatingcompressor, besides the remarkable refinement of the mechanical planningof its different parts, are the mobile seals between piston andcylinder, which undergo a wear proportional to the pressure. In fact anincrease of the pressure jump sustained by a scaling element causes anincrease of the force pressing the rings against the cylindric wall andaccordingly of the wear engendered by the mutual sliding betweencylinders and rings during the reciprocating motion of the piston. I

On the other hand the piston motion, engendered by the crosshead, isnever perfectly coincident with the cylinder axis and this engendersfurther pressures between rings and piston and continuous beddingmotions which contribute, often in a conclusive way, to the failure of aseal.

The work conditions of a seal, both with rings and stuffing box, aremore suitable the closer that the piston motion coincides with thecylinder axis and this condition becomes conclusive of whether thecompressor will operate at very high pressures.

From what has been said it is clear that in the field of the veryhigh-pressure reciprocating compressors the main problem to be solved,besides the use of particular sealing elements, is the perfect alignmentof the piston-cylinder system. Given that the reciprocating motion isengendered by the crosshead, this problem turns into the planning of acrank gear with a crosshead allowing the perfect coincidence of thepiston motion with the cylinder axis.

Now, a departure from the conditions of ideal motion, i.e. a cause ofmisalignment of the piston-cylinder system, is due to the pitchingmotion of the crosshead which transmits to the piston an oscillatorymotion around an axis perpendicular to the one of the cylinder. Saidpitching is mainly due to the moment engendered by the friction from theaction of the connecting rod around the gudgeon and to the momentarising, in the usual crossheads having a single cylindric guidearranged under the piston axis, in connection with the sliding frictionand the inertial forces of the masses dissymmetrically arranged as tothe motion axis. Further causes of misalignment derive from initialoffsets because of deficiencies of working and assembling and fromoffsets engendered, mainly in the plane of crank gear, by thermalexpansions of the crosshead body.

It is therefore the primary object of the present invention to realize acrank gear with a crosshead for operating the piston of reciprocatingcompressors which overcomes the foregoing drawbacks, permitting theoperation of said compressors in fields of very high pressures.

This is obtained by making use of a crosshead having a particular shapewhich surrounds the whole connecting rod and, instead of working onnormal cylindric surfaces, is guided in its reciprocating motion by twostrong wings, arranged on an horizontal plane containing the pistonmotion axis, extending for the whole length of the crosshead but thecentral zone let free in order to allow the rotation of the compressorcrankshaft; The crosshead is further guided by two other wings arrangedin its lower part on a vertical plane containing the motion axis.

It has to be noticed that, given the particular field of application,the crosshead crank gearing is subject to very high pressures andtherefore to drawbacks requiring a strict maintenance.

Another object of the present invention is to provide a crosshead crankgearing, which is of a simple structure and a reduced overall size,allowing quick assembly and easy maintenance.

A further object of the present invention is to provide a crossheadcrank gearing which simultaneously operates the pistons relating topairs of opposite cylinders.

The normal use of reciprocating compressors with pairs of oppositecylinders, whose pistons are operated by a single crosshead, issuggested by the great advantages obtained with such I a symmetricalarrangement. In fact, when a cylinder sucks, the opposite one compressesand the gudgeon and the crosshead crank gearing have therefore to bearonly the difference of the two thrusts, the size of these parts beingtherefore reduced.

Further, the thrusts acting on the gudgeon of the connecting rod smallend, at each turn of the compressor crankshaft, assume equal andopposite values, which, as known, represents the best condition for therunning of the crosshead gudgeon.

In fact, the bushing of the connecting rod small end carries out only asmall oscillation around the crosshead gudgeon and therefore in thelubrication of such a coupling there is no hydrodynamic effect. If, onthe contrary, the thrusts on the gudgeon assume, ateach turn of thecrankshaft equal and opposite values, there is a satisfactorylubrication due to the alternating introductions and ejections betweenthe working surfaces.

With monodirectional thrusts, like the ones of simple cylinders, thereis no such possibility, as the oil is not able to enter between thegudgeon and the bushing, and heavy wear appears quickly.

The invention is illustrated in detail with reference to the encloseddrawings representing a preferred form of realization given only by wayof example, as many structural and technical variants may be thoughtwithout departing from the range ofthe present invention.

FIG. I shows a perspective view of a reciprocating compressor, withpairs of opposite cylinders, making use of the crosshead crank gearingof the present invention.

FIG. 2 is a vertical section of FIG. I, illustrating the position of thecrosshead inside the box and further illustrating the two rodspertaining to the opposite cylinders secured at the middle point of thefront walls of the crosshead, and the flat guides of the two verticalwings of the crosshead.

FIG. 3 is a perspective view of the crank gearing with a crossheadconstructed according to the invention.

FIG. 4 shows a front section of the crank gearing with the crosshead 5of FIG. 3. Referring now more particularly to the accompanying drawings,reference numeral ll designates a steel box or housing which acts as asupport for the two opposed cylinders 2 and 3, and also for thecrankshaft 4 of the compressor, wherethrough the crosshead 5reciprocates. The position of the crosshead 5 inside housing 1, and itsremarkable length which is nearly equal to the length of the housing, isbest seen in FIG. 2. As also shown in FIG. 2 piston rods 6 and 7,pertaining to the opposite cylinders 2 and 3, respectively, are securedat the middle point of the front walls of the crosshead 5, and flatvertical wing plates 10 and 11 of the crosshead.

In accordance with the invention--; the crosshead 5, comprises an upperrigid steel structure 5 and a similar lower rigid steel structure 5"symmetrically secured through a series of bolts 12. Each structurecomprises two similar sides spaced by means of the blocks 13 and 14which are integral parts of the sides at their ends. The connecting rod15 may therefore act in this interspace. As the sides have to bear thestresses exerted by very high pressures, they are reinforced with theribs 16. Each side further presents an opening 17 wherethrough thecrankshaft 4 of the compressor passes. The opening 117 must present asize such as to allow the motion of the crankshaft and therefore thecrosshead reciprocation. Each side further presents a semicircular lobe18 so that the matching of the two structures 5' and 5" engenders acircular hole wherein the gudgeon 19 of the connecting rod small endpasses. Said gudgeon is then secured to the frame formed by said twostructures through resilient stop rings 20 having a conical surfacefitting on the conical ends of the gudgeon (in FIG. 3 it is possible tosee only one stop ring, the other one being arranged on the oppositeside, symmetrically as to axis of the rods 6 and 7).

Between the structures and 5" are introduced two strong steel wingplates 21 and 22 extending on the whole length of the crosshead exceptfor the zone wherein the crankshaft 4 acts. Wing plates 21, 22 protrudefrom both sides of the frame of the two structures 5 and 5", formingthereby four sliding blocks entering corresponding fiat horizontalguides 23 supported by the box 1. Each of plates 21, 22 present athickened portion 24 in the middle point of the front thereof, wheretothe end of the respective piston rods 6, 7 are secured.

The two wing plates 21 and 22 are secured by means of screws (not shown)to the lower structure 5" and are further locked between the twostructures 5 and 5" by a series of bolts 12. As clearly seen in H05. 3and 4, wing plates 21, 22 are thus located in a horizontal planecontaining the motion axis of the pistons coincident with the axis ofthe rods 6 and 7. To the spacing blocks 13 of the lower structure 5" arethen bolted two vertical wings l0 and I1 entering suitable vertical fiatguides 8 and 9 supported by the box 1 (in FlG. 3 and 4 it is possible tosee only the wing 11 and the corresponding guide 9, the wing and theguide 8 being at the other end of the crosshead). The vertical wings l0and ll and the correspond ing guides 8 and 9, as shown in FIG. 4, arearranged on a vertical plane also containing the motion axis of thepistons, i.e. they are arranged symmetrically as to the front section ofthe crosshead. Therefore, when because of the rotation of the crankshaft4 of the compressor the connecting rod 15 transmits a reciprocatingmotion to the frame formed by the two structures 5' and 5", said frame,through the wings 21 and 22, is guided, in its reciprocating motion, byhorizontal flat guides acting on the plane containing the motion axis ofthe pistons. In this manner drawbacks resulting from pitching and on theworking and assembling imperfections are reduced to negligible limits,The oscillations caused by the pitching become smaller as the gap sbetween the guides and the sliding blocks of the crosshead becomesnarrower and the length l of the sliding of the crosshead becomeslarger.

The present crosshead, occupying the most part of the machine width, hasa very remarkable sliding length land the gap s, which in the previousconstruction of crossheads has to be some tenths mm. for allowing thethermal expansion of the sliding body, as a result thereof may bereduced down to a few hundredths mm., since the distance between theguides is only a few cm.; the resulting oscillations, being proportionalto the ratio (s/ I), are therefore as small as possible.

On the other hand, by making use of flat guides coincident with themotion axis of the pistons, it is possible to realize a unit whollysymmetrical as to the horizontal plane containing the motion axis: it ispossible in this way to remove both the pitching alternating moments dueto the frictional forces on the guides and the moments due to theinertial forces of the masses arranged symmetrically as to the motionaxis.

The present crosshead, being guided both in a horizontal plane and in avertical plane containing the motion axis of the pistons through thewings 10 and 11 and the corresponding flat guides 8 and 9, furtherallows the removal of the offsets due to thermal expansions. Theseexpansions, due to the heating, can not alter the motion axis, as theyalways occur symmetrically as to said axis.

lt is also of out that operating with large sized frames, like the oneof the present invention, presents, even making use of hightechnologies, unavoidable geometrical imperfections. In order to reachthe perfection required in aligning the pistoncylinder system, it isgenerally necessary that a manual adjustment be made. It is clear thatsuch as adjustment is easier in the case of flat guides and surfacesthan in the case of the usual cylindrical guides and surfaces: this is afurther advantage of the invention.

Finally the crosshead of the invention allows a quick and easiermaintenance in case of damages. The usual crossheads are shaped in sucha way that the removal of one of their parts causes the remaining partto the unstable or unsupported, this requiring, in case of maintenance,the disassembling of the whole crosshead element by element and ofcourse loss of time. In our case, on the contrary, it IS enough tounscrew the series of bolts 12 and remove only the upper structure 5'for making easily accessible any part of the crosshead.

The unit, in fact, once the structure 5 is removed, does not becomeunstable but remains stabile and rigid, as the wing plates 21 and 22,resting on the corresponding guides 23, support the whole frame as theyare rigidly screwed to the lower structure 5". The alignment of the rodsand guides is not altered as these remain secured to the lower structure5".

lclaim:

1. ln crank gearing mechanism for operating a pair of opposed pistonsadapted to reciprocate in a corresponding pair of opposed cylinders of ahigh-pressure reciprocating compressor or the like, including a housingstructure supporting each of said opposed cylinders, the compressorcrankshaft, a reciprocating crosshead actuating said opposed pistons,and a connecting rod connecting said crankshaft with said crosshead, theimprovement therein which comprises: said crosshead comprising a pair ofidentical upper and lower frame sections fixedly removably securedtogether in opposed relationship to form a rigid crosshead framestructure extending longitudinally over a major portion of the length ofsaid housing structure, each of said upper and lower frame sectionsincluding a pair of spaced, vertically extending sidewalls,

said sidewalls of said frame sections having identical, op-

posed first and second openings therein, whereby when said upper andlower frame sections are secured together in opposed relationshipthespaced sidewalls of said frame structure are adapted to receive saidconnecting rod therebetween, the opening formed by said first openingsis adapted to rotatably receive the connecting rod gudgeon therein, andthe opening formed by said second openings is adapted to receive saidcompressor crankshaft therein and to accommodate the movement thereof,

each of said upper and lower frame sections further includingreinforcing spacing block means secured between said sidewalls at theopposite ends thereof; and a pair of plate members secured between saidupper and lower frame sections,

each of said plate members having an enlarged central portion enclosedby said frame sidewalls and flat wing portions extending horizontallyoutwardly from each of said frame sidewalls,

said central portions of said plate members adapted to fixedly house therespective piston rods of said opposed pistons in the horizontal planedefined by said wing portions of said plate members, and

said plate wing portions extend along the length of said crosshead framestructure from the ends thereof to said opening receiving saidcompressor crankshaft.

2. Crank gearing mechanism as defined in claim 1 wherein said crossheadfurther includes a pair of vertical flat wing plate portions secured tosaid lower frame section in a vertical plane containing the motion axisof said piston rods.

3. Crank gearing mechanism as defined in claim 1, wherein said sidewallsof said upper and lower frame sections of said crosshead frame structureinclude reinforcing rib means.

4. Crank gearing mechanism as defined in claim 1, wherein said housingstructure includes horizontal guide means slidable receiving saidhorizontal plate wing portions therebetween, to thereby guide saidcrosshead frame structure in a horizontal plane which includes themotion axis of said piston rods. 14

5. Crank gearing mechanism as defined in claim 2, wherein said housingstructure includes vertical guide means slidably receiving said verticalwing plate portions therebetween, to thereby guide said frame structurein a vertical plane which includes the motion axis of said piston rods.

1. In crank gearing mechanism for operating a pair of opposed pistonsadapted to reciprocate in a corresponding pair of opposed cylinders of ahigh-pressure reciprocating compressor or the like, including a housingstructure supporting each of said opposed cylinders, the compressorcrankshaft, a reciprocating crosshead actuating said opposed pistons,and a connecting rod connecting said crankshaft with said crosshead, theimprovement therein which comprises: said crosshead comprising a pair ofidentical upper and lower frame sections fixedly removably securedtogether in opposed relationship to form a rigid crosshead framestructure extending longitudinally over a major portion of the length ofsaid housing structure, each of said upper and lower frame sectionsincluding a pair of spaced, vertically extending sidewalls, saidsidewalls of said frame sections having identical, opposed first andsecond openings therein, whereby when said upper and lower framesections are secured together in opposed relationship the spacedsidewalls of said frame structure are adapted to receive said connectingrod therebetween, the opening formed by said first openings is adaptedto rotatably receive the connecting rod gudgeon therein, and the openingformed by said second openings is adapted to receive said compressorcrankshaft therein and to accommodate the movement thereof, each of saidupper and lower frame sections further including reinforcing spacingblock means secured between said sidewalls at the opposite ends thereof;and a pair of plate members secured between said upper and lower framesections, each of said plate members having an enlarged central portionenclosed by said frame sidewalls and flat wing portions extendinghorizontally outwardly from each of said frame sidewalls, said centralportions of said plate members adapted to fixedly house the respectivepiston rods of said opposed pistons in the horizontal plane defined bysaid wing portions of said plate members, and said plate wing portionsextend along the length of said crosshead frame structure from the endsthereof to said opening receiving said compressor crankshaft.
 2. Crankgearing mechanism as defined in claim 1 wherein said crosshead furtherincludes a pair of vertical flat wing plate portions secured to saidlower frame section in a vertical plane containing the motion axis ofsaid piston rods.
 3. Crank gearing mechanism as defined in claim 1,wherein said sidewalls of said upper and lower frame sections of saidcrosshead frame structure include reinforcing rib means.
 4. Crankgearing mechanism as defined in claim 1, wherein said housing structureincludes horizontal guide means slidable receiving said horizontal platewing portions therebetween, to thereby guide said crosshead framestructure in a horizontal plane which includes the motion axis of saidpiston rods. 14
 5. Crank gearing mechanism as defined in claim 2,wherein said housing structure includes vertical guide means slidablyreceiving said vertical wing plate portions therebetween, to therebyguide said frame structure in a vertical plane which includes the motionaxis of said piston rods.